Honeywell "Y" Plan System

[Drogna]

Hi - I'm a newbie here so please be gentle!

I've got a Honeywell Sundial "Y" plan system installed in my house (probably about 20 years old now) and this evening the heating's gone off! The thermostat in the lounge still clicks but it doesn't fire up the boiler. I can still get hot water, however the digital display on the programmer (located in the airing cupboard - Honeywell ST7000) is completely blank, the immersion fused spur still has power to it, so I'm guessing it's not a blown fuse and my instincts are telling me the programmer MAY need replacing??? Am I looking in the right area here?

Thanks in advance for your assistance.

 

[ChrisR]

Depends where the programmer gets its power from, dunnit. It shouldn't be on the same fuse as the immersion heater!

 

[bab]

u might still have hot water cos its from be 4 the boiler stopped or even the immersions on. is the boiler or pump working or is the whole system down?

 

[Drogna]

Nope - you're quite right, it doesn't! According to the literature it comes from a "sundial wiring centre"! Doesn't help me much sadly!

THe pump was working when I checked earlier, but its not now! The immersions off, we tend not to use it. The boiler is stil working.

 

[corgiman]

Highly unlikely, as ChrisR says, that the immersion heater spur also powers your boiler and controls, if it does call a sparks straight away to rectify this.

Dont suppose a bread bin or something has been pushed up aganst a switch in the kitchen or something similar in the airing cupboard has it

Dont laugh you'd be surprised how many jobs i go to and find that lol

 

[Drogna]

First thing I checked Corgiman! The airing cupboard was a little full, but not that it pressed any of the buttons. My main concern is the blank screen on the programmer - can't seem to get any life into that at all!

 

[corgiman]

its probably not getting electris mate.

Is there not a swtich any where that you dont have a clue what its for?

 

[Drogna]

Can't find any switches but I've just discovered a battery panel with a couple of AA's in it (use by July 1997 - might replace those and see what happens)!

 

[Drogna]

New batteries and the display is back to life - right, gonna have another tinker now, reckon I've got this sussed now. Thank you so much for all your help guys, very much appreciated!

 

[bab]

Think u'll find those r only the back up batteries for setting saver so it sounds like u still have no power to ya clock. I could be wrong not had a lot to do with that programmer . Some digi roomstats dont work when the AA,s go. Its bizarr.

 

[Drogna]

Thanks for that bab - I'll check that tomorrow, but at the moment I'm glad I've got some heat for tonight!

 

[bab]

If its up an running it sounds as if it was onloy the batteries stopping the programmer. I'd leave it if its ok 4 now.

 

[Drogna]

Pride comes before a fall! I had a "luke warm" night as the rads never fully came on, although the thermostat triggered the boiler and the pump was working well - still it was better than nothing. So now I have a couple of questions:

1) Let's assume that the programmer is battery powered, would the system have worked without the programmer when the batteries died? If not, then that leads me on to.....

2) The current problem would suggest that the mid position valve (Honeywell V4073A) has now jammed in a position that gives me hot water and only a small amount getting to the heating system - could it be that the electrics (if applicable) that controlled the programmer also are controlling the valve and therefore I have a much bigger problem? My gut feeling is to replace the valve, but would it be worth just replacing the electric pack first?

I appreciate any advice that's forthcoming! Cheers again.

 

[Softus]

1) Let's assume that the programmer is battery powered

Unwise assumption, because it's so unlikely.

would the system have worked without the programmer when the batteries died?

If the batteries simply power the display, then yes, if not, then no.

2) The current problem would suggest that the mid position valve (Honeywell V4073A) has now jammed in a position that gives me hot water and only a small amount getting to the heating system

It's extremely rare to have two faults at once, so it's more likely that you're misdiagnosing at least one of them.

...could it be that the electrics (if applicable) that controlled the programmer also are controlling the valve and therefore I have a much bigger problem?

The MZV is mains powered; I would put money on your programmer also being mains powered (because I can't find a reference to ST7000 at the moment).

My gut feeling is to replace the valve, but would it be worth just replacing the electric pack first?

Ignore all of your gut feelings - you don't have enough experience of heating systems to do this without systematic fault-finding.

The first thing to establish is whether or not your programmer is working:

1. Does the boiler switch on and off under control of the programmer?
2. Does the pump switch on and off under control of the programmer (although be aware that some boilers will cause the pump to run periodically at what you'd think would be non-programmed times).

If yes to both, then move on...

3. Does the MZV operate according to your room thermostat and cylinder thermostat?

If the MZV is not operating as you would expect, then determine whether or not the electrical supply to it behaves as you would expect according to your room thermostat and cylinder thermostats.

If you don't know what to expect from a 3-port MZV, then search the forum. If you can't find an explanation then post here again.

Newbie or not, there's no reason for you to guess or to make assumptions.

 

[Drogna]

Softus - thanks for your input.

1. The boiler does switch on and off under the control of the programmer - tried this last night with the new batteries in and it was working fine.

2. The pump also switches on and off under the control of the programmer.

3. No, the MZV is not reacting to any changes from the thermostats.

The MZV doesns't seem to be working as usually it makes a noise though the pipework when it engages, and this noise is distinctly missing - also, when the radiators are working you can hear the water running through them, which isn't occuring at the moment.

I moved the switch on the bottom of the MZV accross to manual, and then returned it to the auto position - however, the MZV seems to have stayed in position - I know there's a return spring in there but I'm not 100% that it's doing it's job.